The present invention relates to a disc brake caliper for an automotive vehicle such as a car or a motorcycle, and in particular, the invention relates to a caliper which includes both a service and a parking brake facility. A caliper of this kind, which is operable in both service and parking brake modes, can be termed an “integral disc brake caliper ” and that terminology will be used to describe such a caliper hereinafter throughout this specification.
Integral disc brake calipers have been devised in the past and these typically have involved a hydraulic service brake actuator including a hydraulically driven piston, and a parking brake actuator which acts through a suitable mechanism to drive the piston in the manual parking brake mode. The arrangement is such that the hydraulic actuator is operable to shift the piston outwardly of a piston cylinder in which it is disposed, to engage a disc brake pad and to push the pad into engagement with the disc rotor. By known means, engagement of the brake pad with the disc rotor causes a second brake pad disposed on the opposite side of the rotor to shift into engagement with that side of the rotor and thus the rotor becomes sandwiched between the brake pads, producing a braking effect.
The parking brake actuator in such calipers is operable to produce the same movement of the disc brake pads to sandwich the rotor and in the known arrangements, the parking brake actuator has been operable to displace the piston of the hydraulic actuator into engagement with the respective brake pad. To achieve that displacement, the parking brake actuator has been disposed within, or partly within the cylinder which houses the piston, to act on the piston when the parking brake is to be actuated. In this type of arrangement, the construction of the caliper can be quite complicated in order to accommodate the parking brake actuator partly or fully within the piston cylinder and in particular, the complicated nature of the caliper arises somewhat because accommodation of the parking brake actuator in the piston cylinder introduces at least an additional leakage path, so increasing the likelihood of leakage from the piston cylinder. Because there is a need to properly seal against the increased likelihood of leakage this invariably complicates the construction and reliability of the caliper.
In a different arrangement which is known to the applicant, the parking brake actuator is arranged to act on the piston, but outside of the piston cylinder. This arrangement advantageously alleviates the difficult and complicated sealing requirements of the other known forms of integral disc brake calipers, but the arrangement still requires a complicated construction for rerouting or redirecting the eccentric actuating load which arises in such an arrangement, back to the piston, which detracts from its usefulness, and increases its potential for failure. The arrangement lacks stiffness and therefore the displacement efficiency of the parking brake actuator is poor. Accordingly, there is a need for a greater input displacement to achieve the piston displacement necessary to properly apply the parking brakes. Further, the greater displacement required to apply the parking brakes can mean that the time taken for application thereof, is increased.
A further disadvantage in relation to each of the aforedescribed actuators is that failure of one of the service or parking brake actuators can affect the other. This may occur for one or more of a variety of reasons. For example, if the piston of the hydraulic actuator jams, then neither of the service or parking brakes will be operable. Thus, the shared componentry of the actuators can compromise the integrity of the caliper.